1. Field of the Invention
The invention relates to ordnance such as an explosive blast shield. More particularly, the invention relates to a composite panel having explosive blast frequency mitigating components. The invention is a method of mitigating specific blast frequencies that are damaging to human tissue.
2. Discussion of the Related Art
Explosive blast attack against people in open areas and in buildings continues to be a challenge in the armor arts. The primary defense against militant blast attack in open areas around buildings is a perimeter vehicle barrier such as a concrete wall. However, explosive blast generates a pressure wave that continues past a perimeter barrier. If a large explosive load is detonated, the pressure wave can travel with sufficient force to cause traumatic brain injury to people behind concrete walls and inside buildings.
Mechanisms that result in traumatic brain injury have been investigated. Suggested mechanisms include blast compression of body cavities which generate vascular pulses transmitted to the brain, skull deflection, explosively-generated, piezoelectric charge formation from loading on the bones of the skull, blast induced cerebral spinal fluid cavitation and direct transmission of pressures and accelerations sufficient to induce injury into the brain. G. J. Cooper investigated the connection between blast frequencies and effects on humans. He found, that the frequency range of 1000 and 3000 Hz is particularly damaging to lung tissue. This damaging frequency range is identified in the Drawing as the Cooper Injury Range. This work is reported in G. J. Cooper “Protection of the Lung from Blast Overpressures by Thoracic Stress Wave Decouplers”, Journal of Trauma: Injury, Infection, and Critical Care, vol. 40, no. 3 (1996), incorporated, herein by reference. One method of reducing some of the injury to humans would be to limit exposure to blast frequencies in this range.
Investigations of potential barrier panels have identified blast wave couplers and de-couplers. Simple soft foams increased blast damage to the thorax. This was attributed to coupling the blast more effectively with the body. However when high impedance materials, such as high Young's modulus and/or density materials, were used as a facing and backed by a low impedance material such as soft foam, a blast wave decoupling was observed. Decoupling resulted in less internal blast damage to the human body.
Investigators have found that textiles exhibit differing behaviors in response to blast pressure loadings. Vests comprising some textile materials altered blast pressure loading on the thorax. One study found that a ballistic fabric vest increased blast associated injury. Another study indicated that blast pressure loading on the body could be reduced if textile fibers were pre-compressed instead of being loose.
There is a continuing need in the art of personnel protection for an effective explosive blast shield. To be fully effective in protecting human tissue, any shield must protect against the force of an explosive blast pressure wave and particularly limit exposure to the most damaging blast frequencies.